Carburetor fuel metering valve with mid-range fuel adjustment

ABSTRACT

A carburetor and carburetor fuel metering valve for an internal combustion engine. The metering valve has slidably interfitting valve sleeves which are relatively rotatable by adjustment of the carburetor throttle valve and contain fuel metering ports whose overlap defines a fuel metering orifice having an area which is progressively varied by such relative rotation to meter fuel to the engine in relation to air flow. The metering valve includes at least two sets of fuel metering ports which may be selectively disposed in fuel metering relation to provide a mid-range fuel adjustment independent of throttle setting. The metering valve may also include an idling fuel adjustment for adjusting the effective orifice area of each metering port set and thereby fuel flow in the idling setting of the throttle valve and a high speed fuel adjustment for adjusting fuel flow in the high or full speed setting of the throttle valve.

United States Patent [191 Perry Sept. 9, 1975 CARBURETOR FUEL METERINGVALVE WITH MID-RANGE FUEL ADJUSTMENT John C. Perry, 971 Mira Mar DrVista, Calif. 92083 Filed: July 20, 1973 Appl. No.: 381,013

lnventor:

References Cited UNITED STATES PATENTS [/1973 Perry 261/41 PrimaryExaminer-Henry T. Klinksiek ABSTRACT A carburetor and carburetor fuelmetering valve for an internal combustion engine. The metering valve hasslidably interfitting valve sleeves which are relatively rotatable byadjustment of the carburetor throttle valve and contain fuel meteringports whose overlap defines a fuel metering orifice having an area whichis progressively varied by such relative rotation to meter fuel to theengine in relation to air flow. The metering valve includes at least twosets of fuel metering ports which may be selectively disposed in fuelmetering re lation to provide a mid-range fuel adjustment independent ofthrottle setting. The metering valve may also include an idling fueladjustment for adjusting the effective orifice area of each meteringport set and thereby fuel flow in the idling setting of the throttlevalve and a high speed fuel adjustment for adjusting fuel flow in thehigh or full speed setting of the throttle valve.

10 Claims, 14 Drawing Figures 28 35 A 31 24 30 R AM I l l i F -2sM P 20-I I is G (12 PATENTEB an a IHlb SHEET Fig. 4

CARBURETOR FUEL METERING VALVE WITH MID-RANGE FUEL ADJUSTMENT BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relatesgenerally to the field of carburetors for gasoline powered engines andmore particularly to a novel carburetor fuel metering valve andcarburetor embodying the valve.

2. Discussion of the Prior Art As will become evident from the ensuingdescription, the fuel metering valve of this invention may be used toadvantage in a variety of gasoline carburetors. However, the valve isdesigned primarily for use in the carburetors of my prior Pat. Nos.3,547,415 and 3,7l L068. For this reason, the valve will be disclosed inconnection with the latter carburetors.

The carburetors of my prior patents have a body containing a rotarythrottle valve barrel with a transverse passage which defines the throatof an induction air Venturi having an inlet in the body at one end andan outlet in the body at the other end of the barrel passage. Rotationof the valve barrel between idling and high speed positions regulatesair flow through the Venturi and hence the vacuum in the Venturi throat.

Extending through the carburetor body on the axis of the throttle valvebarrel is a bore containing a fuel metering valve including a pair ofslidably interfitting valve sleeves. The inner end of the inner valvesleeve projects axially through the valve barrel into its Venturi throatpassage to provide a fuel jet opening to the passage and is fixed to thebarrel for rotation with the barrel.

Rotation of the throttle valve between its idling and high speedpositions rotates the inner valve sleeve relative to the outer valvesleeve between idling and high speed positions. Opening through thesleeve walls are a pair of circumferentially overlapping fuel meteringports whose overlap area varies progressively to regulate fuel flow tothe Venturi fuel jet upon rotation of the inner valve sleeve between itsidling and high speed positions with the throttle valve relative to theouter valve sleeve.

The carburetors of my prior patents are provided with idling and highspeed fuel adjustments for regulating fuel flow to the fuel jetindependently of the throttle valve setting. My prior carburetors thuspermit optimization of the air/fuel ratio to the engine within itsidling and full speed operating ranges. These carburetors, however, lacka mid-range fuel adjustment, that is, an adjustment for regulating theair/fuel ratio to the engine independently of throttle valve setting, inthe midrange of engine operation between idling and full speed. Amid-range fuel adjustment is desirable to compensate or correct foraltitude changes, differing engine operating characteristics, and otherfactors, to permit breaking in of a new engine with a rich air/fuelmixture, and for other reasons.

SUMMARY OF THE INVENTION This invention provides an improved carburetorand carburetor fuel metering valve having such a mid-range fueladjustment. The improved fuel metering valve is basically similar to themetering valves of my prior patents and comprises interfittingrelatively rotatable valve sleeves containing fuel metering ports whoseoverlap region defines a fuel metering orifice whose area is variedprogressively by relative rotation of the sleeves.

The throttle valve and inner fuel metering valve sleeve are rotatable inunison by the throttle arm between idling and high speed positions toregulate air flow through the carburetor and meter the fuel in relationto the air flow in the same manner as in the carburetors of my priorpatents. Rotation of the ow ,r valve sleeve relative to the inner valvesleeve provides an idling fuel adjustment independent of throttlesetting, and adjustment of a needle valve extending through the innersleeve provides a high speed fuel adjustment, also in the same manner asin my patented carburetors.

According to a primary feature of this invention, the fuel meteringvalve has at least two sets of fuel metering ports which may be utilizedselectively to meter the fuel. The particular fuel metering valvedescribed, for example, has three such metering port sets. Thesemetering port sets are sized such that shifting or adjusting themetering valve from one of these metering port sets to the otherprovides a mid-range fuel adjustment which regulates fuel flowindependently of throttle valve setting in the mid-range between idlingand high speed to correct for differences in altitude and/or enginecharacteristics, permit break-in engine operation with a rich fuel/airmixture, or other reasons.

According to another feature of the invention, the metering sleeve portsare uniquely shaped to extend the total idling adjustment angle or rangeof the outer metering valve sleeve. This permits finer and more accurateadjustment of the idling fuel flow at each midrange adjustment settingof the outer sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a smallgasoline powered engine, such as a model airplane engine, equipped witha carburetor embodying an improved fuel metering valve according to theinvention;

FIG. 2 is an enlarged view of the carburetor looking in the direction ofthe arrows on line 22 in FIG. 1',

FIG. 3 is a further enlarged section through the carburetor;

FIG. 4 is a section taken on line 4-4 in FIG. 3;

FIG. 5 is an enlarged section through the fuel metering valve taken online 5-5 in FIG. 4;

FIGS. 6a, 6b, 6c illustrate flat developments of the fuel metering portsin the outer sleeve of the fuel metering valve;

FIG. 7a is an enlarged fragmentary front elevation of the inner sleeveof the fuel metering valve illustrating its fuel metering port;

FIG. 7b is a side elevation of the valve sleeve in FIG. 7a;

FIG. 8 is an enlarged fragmentary elevation of the assembled valvesleeves of the fuel metering valve illustrating the sleeves in onemid-range adjustment setting; and

FIGS. 9a, 9b, 9c are enlarged semi-diagrammatic views illustrating thefuel metering action of the fuel metering valve during throttle valveadjustment between idling and full speed positions with the valvepositioned in one mid-range adjustment setting.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawings illustrate acarburetor 10 which is identical, except for its fuel metering valve, tothe carburetors of my prior patents, mentioned earlier. Carburetor 10 isshown mounted on a gasoline engine 11. In this instance, the engine is asmall two-cycle gasoline engine of the type used on radio controlledmodel airplanes, boats, and the like. Carburetor 10 has a body 12through which extends an induction air passage P defining a Venturihaving an inlet 1, an outlet 0, and an intervening throat T. Mountedwithin the passage P is a throttle valve V, which is movable betweenidling and high speed positions through a series of mid-range positionsto regulate induction air flow through the passage. A fuel jet Jprojects into the carburetor Venturi throat T. Fuel jet J communicatesto a fuel inlet F on the body through the improved fuel metering valveV,, of this invention. This valve has variable area fuel metering meansM through which fuel flows from the inlet to the jet. About the fuelmetering valve is an annular fuel reservoir R communicating the fuelinlet F to the fuel metering means M. The throttle valve V, and themetering valve V are interconnected for adjustment of these valves inunison to regulate fuel flow to the fuel jet J concurrently withregulation of induction air flow through the carburetor Venturi.

Embodied in the metering valve V is a low speed fuel adjustment A and ahigh speed Fuel adjustment A,,. These adjustments permit regulation offuel flow to the fuel jet J independently of the setting of the throttlevalve V and, as will be explained presently, are set with the throttlevalve in its idling and high speed positions, respectively, to attainoptimum fuel/air mixtures at these settings. According to a primaryfeature of this invention, the fuel metering valve embodies a midrangeadjustment A for regulating fuel flow to the fuel jet independently ofthrottle valve setting over the midportion of the throttle adjustmentrange to attain a desired fuel/air mixture in the midoperating range.

The carburetor 10 is installed on the engine 11 by coupling thecarburetor outlet to the engine air intake. During engine operation,induction air flow to the engine occurs through the carburetor Venturi.Fuel flow occurs from the carburetor fuel inlet F, through the meteringvalve V,,,, to the fuel jet J from which the fuel is discharged into theVenturi throat T to mix with the induction air. The throttle V, and thevalve V are adjustable in unison to concurrently regulate induction airflow and fuel flow through the carburetor. The low speed fuel adjustmentA and high speed fuel adjustment A are set with the throttle valve V, inits idling position and its high speed position, respectively, toprovide optimum fuel air mixtures at these throttle settings. Themid-range fuel adjustment A is set to provide the optimum fuel airmixture over the intervening mid-operating range of the engine.

Referring now in greater detail to the drawings, the body 12 of thecarburetor has a generally blocklike configuration and may be machinedor injection molded from plastic or metal. Extending centrally throughthe body is a bore 13, one end of which is counterbored at 14. Rotatablyfitted within the counterbore 14 is a valve barrel 15 which constitutesthe throttle valve V,. Valve barrel 15 has an outer end facesubstantially flush with the adjustment end face of the carburetorhousing 12. Seating against this end face of the valve barrel is athrottle arm 16. Throttle arm 16 is firmly clamped to the valve barrel15 by a screw 17, whereby the barrel may be rotated by the applicationof a force to the outer end of the arm. Extending through the outer endof the thronle arm 16 are a pair of holes 16a, l6b for receivingoperating links 18a, 18b. These links will be referred to againpresently.

Extending diametrically through the throttle valve barrel 15 is a bore20 communicating a pair of diametrically opposed openings 21 and 22 atopposite sides of the carburetor body 12. Bore 20 and openings 21, 22collectively define the carburetor Venturi and individually define,respectively, the Venturi throat T, inlet 1, and exit 0. The inlet andexit openings 21, 22 have inwardly convergent tapers and diameters attheir inner ends which are substantially equal to the diameter of thevalve barrel throat bore 20. in the particular embodiment of theinvention illustrated, the carburetor body 12 is injection molded in onepiece, preferably from plastic, and the inlet opening 21 has a conicallytapered wall 21a which is molded integrally with the body. The exitopening 22 has an externally cylindrical wall 22a formed by a sleevewhich is fabricated separately from the carburetor body and is pressedfitted in or otherwise secured to the body.

Fuel metering valve V has a pair of slidably interfitting metering valvesleeves 23, 24. lnner sleeve 23 extends coaxially through and is firmlysecured at one end to the inner end of the throttle valve barrel 15.This end of the inner valve sleeve projects into the valve barrel throatbore 20 to form the fuel jet 1. The opposite end of the inner valvesleeve extends centrally through the carburetor body bore 13 and beyondthe adjacent end face of carburetor body. The outer valve sleeve 24 fitsrotatably on the inner valve sleeve within the body bore 13 and has anouter diameter substantially smaller than the bore to provide the fuelreservoir R about the outer sleeve, as explained later.

The fuel metering means M of the fuel metering valve V,, comprises asingle fuel metering port 25 in the wall of the inner valve sleeve 23and three fuel metering ports 26L, 26M, 26H in the wall of the outervalve sleeve 24. The inner sleeve port 25 is essentially a rectangularport with circumferentially spaced boundary edges 25a and 25b. Eachouter sleeve port 26L, 26M, 261-! has a relatively narrow slit-likecentral portion 27a extending circumferentially of the outer valvesleeve and terminating at one end in an enlarged opening 27b and as itsother end in a boundary edge 270. For reasons which will become apparentas the description proceeds, the central portion 270 of each port 26L,26M, 26H is hereafter referred to as its mid-range portion, the enlargedopening 27 b of each port as its high speed portion, and the oppositeend of each port as its idling portion.

The three ports 26L, 26M, 261-1 are uniformly spaced circumferentiallyabout the outer valve sleeve 24 and are located in a common plane normalto the sleeve axis. These three ports are identical except for the widthof their mid-range portions 27a. in this regard, it will be observedthat the mid-range portion of port 26L is slightly narrower and that ofport 261-! is slightly wider than the mid-range portion of the port 26M.

As will be explained in more detail presently, the outer metering valvesleeve 24 is rotatably adjustable to locate any one of its threemetering ports 26L, 26M, 26H in fuel metering relation to the innervalve sleeve port 25, wherein the outer sleeve port is disposed inoverlapping relation to the inner sleeve port. This adjustment of theouter sleeve is referred to as its midrange adjustment and thecorresponding three positions of the outer sleeve are referred to as itsmid-range adjustment positions or settings. Moreover, the outer valvesleeve has a limited range of rotatable adjustment at each mid-rangesetting. This latter adjustment is hereafter referred to as a low speedor idling adjustment.

As will also be explained in greater detail later, the outer meteringvalve sleeve 24 is initially adjusted to and then left in optimummid-range and idling adjustment positions or settings. During actualcarburetor operation, the outer sleeve remains fixed in these optimumsettings, and the inner valve sleeve 23 rotates relative to the outersleeve to meter fuel to the engine in accordance with the setting of thethrottle valve.

The idling and mid-range fuel adjustments A,, A of the valve V,,comprises a peripherally serrated disc 28 rigidly secured to the outerend of the outer metering valve sleeve 24. This disc projects edgewisebeyond two opposite side faces of the carburetor body 12, as shown inFIG. 4, to permit rotation of the disc by hand to turn the outer valvesleeve relative to the inner valve sleeve 23. The inner face of the discseats slidably against the adjustment end face of the carburetor body.The outer end of the inner valve sleeve 23 projects a small distancebeyond the outer face of the disc and is externally circumferentiallygrooved to receive a snap ring 30.

Surrounding the outer valve sleeve 24 of the metering valve V,, are apair of 0 rings 31. These 0 rings are contained within circumferentialgrooves in a pair of radially enlarged axially spaced shoulders 32 whichare integrally formed on the outer valve sleeve. 0 rings 31 bear againstthe wall of the carburetor body bore 31 to define with this wall and theouter valve sleeve the annular fuel reservoir R.

The high speed adjustment A of the fuel metering valve comprises aneedle valve 33 which is threaded in the outer end of the inner valvesleeve 23. The inner end of this needle valve is reduced in diameter toprovide the valve needle 33a proper and an annular space about theneedle. Valve needle 33a extends through the fuel passage in the innervalve sleeve, past the valve sleeve metering orifices 26L, 26M, 26H,into the opening through an annular valve seat 34 adjacent the fueljet 1. Surrounding the needle valve between its knurled knob and the lowspeed adjustment disc 28 is a compression spring 35. This spring exertsaxial pressure on the knob to effect frictional retention of the needlevalve in its current setting.

Referring now to FIG. 1, it will be observed that the carburetor I0 ismounted on the engine 11 in the same way as the conventional modelengine carburetor. Thus, the carburetor outlet sleeve 22a is coupled tothe engine air intake so that induction air flow to the engine occursthrough the carburetor Venturi passage P. The carburetor throttle arm 16is connected to a throttle actuator, such as a servo actuator, throughthe link 180. Link 18b connects the throttle arm to the usual pivotedexhaust shutter 11a on the engine 11 for adjustment of the shutter andcarburetor throttle valve in unison. The curburetor fuel inlet isconnected to a fuel tank (not shown) through fuel line 36.

From the description to this point, it is evident that the outer sleeve24 of the fuel metering valve V, is rotatable by means of its disc 28relative to the inner valve sleeve 23 and throttle valve to locate anyselected outer sleeve fuel metering port 26L, 26M or 26H in fuelmetering position wherein the selected outer port and the inner port 25are disposed in overlapping relation to form a fuel metering orifice.Rotation of the throttle arm 16 rotates the inner valve sleeve andthrottle valve in unison and the inner sleeve relative to the outervalve sleeve. The outer valve sleeve is frictionally held againstturning with the inner valve sleeve during rotation of the inner sleeveand throttle valve by the throttle arm. As mentioned earlier andexplained in detail below, the outer valve sleeve is rotated relative tothe inner valve sleeve to effect the idling and mid-range fueladjustments for regulating fuel flow independently of throttle setting.Rotation of the inner valve sleeve with the throttle valve by rotationof the throttle arm regulates fuel flow in relation to induction airflow to regulate engine power and speed.

The above idling and mid-range adjustments and fuel regulating actionsof the fuel metering valve V will now be explained in more detail byreference to FIGS. 8-9. The fuel metering ports 25, 26L, 26M, 26H of themetering valve have already been described and hence need not beredescribed at this point. Suffice it to say that FIGS. 8 and 9 show theouter metering valve sleeve 24 in one of its three mid-range adjustmentpositions, specifically the adjustment position wherein its midside fuelmetering port 26M is located in fuel metering position, i.e., inoverlapping relation to the inner valve sleeve port 25. In thisposition, the ports define a fuel metering orifice 0 through which fuelflow occurs from the fuel reservoir R to the fuel jet J during engineoperation.

As explained above, during engine operation, the throttle valve 15 andinner fuel metering valve sleeve rotate in unison with the throttle arm16 and relative to the outer valve sleeve 24 to regulate fuel flow tothe engine relation to air flow to the engine. In this regard, it willbe observed in FIGS. 8 and 9 that during rotation of the inner valvesleeve relative to the outer valve sleeve 24, the boundary edge 25a ofthe inner sleeve port 25 moves back and forth along the outer sleeveport currently in fuel metering position, i.e., port 26M. This back andforth movement of the edge along the outer port varies the effectivearea of the fuel metering orifice O and hence the rate of fuel flowthrough the orifice.

FIG. 9A shows the position occupied by the inner port boundary edge 25awhen the throttle valve I5 and inner valve sleeve 23 are in their fullspeed or full open position. In this position, the inner sleeve port 25uncovers the entire outer sleeve port 26M and hence the metering orificeO has maximum area. Maximum fuel flow thus occurs to the engine.Rotation of the throttle valve and inner valve sleeve from the full openor full speed position of FIG. 9A to the idling position of FIG. 9Cresults in movement of the inner port boundary edge 25a along the outermetering port 26M toward its tapered end 270. Port 26M is therebyprogressively covered by the inner valve sleeve 23 and the fuel meteringorifice O is progressively reduced in area to progressively reduced fuelflow to the engine to the idling level. Rotation of the throttle valveand inner valve sleeve from their idling position to full open positionhas the opposite effect of progressively increasing fuel flow to theengine.

As noted earlier, the idling fuel adjustment A, involves rotatableadjustment of the outer metering valve sleeve 24 with the throttle valve15 and inner valve sleeve 23 in idling position (FIG. 9c). Thisadjustment moves the tapered boundary edge 270 of the outer sleeve portcurrently in fuel metering position (i.e., port 26M) back and forthacross the boundary edge 25a of the inner sleeve port 25 to vary thearea of the fuel metering orifice O and hence fuel flow to the engine atidling. in connection with this adjustment, it is significant to notethat the port boundary edges 25a, 27c are inclined in oppositedirections to intersect one another. Accordingly, in the idlingadjustment range, the metering orifice O is tapered, as shown. Thistapered orifice configuration effectively extends the idling adjustmentrange, as compared to the adjustment range which would exist if theboundary edges 250, 270 were parallel, thereby permitting more preciseidling fuel adjustment. The idling fuel adjustment is set to attain anoptimum air/fuel ratio to the engine and hence optimum engine operationat idling.

The mid-range fuel adjustment A, involves rotation of the outer meteringvalve sleeve 24 to locate one of its fuel metering ports 26L, 26M, 26Hin fuel metering position relative to the inner valve sleeve port 25. Inthis regard, it will be observed that the central, midrange portions 270of the three ports 26L, 26M, 26H differ in width. Accordingly,adjustment of the outer valve sleeve from one mid-range adjustmentsetting to another effectively varies the area of the fuel meteringorifice over the mid-operating range of the engine independently ofthrottle valve setting. Thus, rotation of the outer valve sleeve fromits setting of FIGS. 8 and 9 to the setting in which port 26L is locatedin metering position reduces fuel flow to the engine in any givenmid-range throttle valve setting. Rotation of the outer valve sleeve tothe setting in which port 26H is located in metering position increasesthe fuel flow in any given mid-range throttle valve setting. Thismid-range fuel adjustment is set to attain the optimum air/fuel ratioand hence engine operation over the mid-operating range and may beutilized, for example, to compensate for different altitudes,atmospheric conditions, to provide a rich mixture for engine break-inand for other purposes.

Needle valve 33 is set to attain optimum air/fuel ratio and engineoperation at full speed, where the throttle valve and inner valve sleeve23 occupy their full open position. ln this position, the entire outerfuel metering port 26L, 26M, 26H, including its high speed enlargementor aperture 27b, is uncovered. This enlargement provides additional fuelto the engine in the full open position of the throttle valve 15 to thesame mannet and for the same purpose as the high speed port in the fuelmetering valve of my prior Pat. No. 3,71 1,068. The needle valve 33 iseffective to regulate the fuel flow at this full throttle position inthe same manner as in the latter patent.

What is claimed as new in support of Letters Patent is:

l. A carburetor fuel metering valve comprising:

a pair of slidably interfitting valve sleeves which are relativelyrotatable to a plurality of mid-range fuel adjustment settings and arerelatively rotatable at each mid-range setting through an operating fuelmetering range between idling and full speed positions,

said sleeves having fuel metering ports which overlap at each mid-rangesetting to form a fuel metering orifice whose effective area is variesby relative rotation of the sleeves through the corresponding fuelmetering range, and said sleeves being relatively rotatable tocorresponding fuel metering positions within the fuel metering rangesand the fuel metering ports being so sized that the effective orificeareas differ at said corre sponding fuel metering positions. 2. Acarburetor fuel metering valve according to claim 1 wherein.

said valve sleeves are relatively rotatable to two midrange settings toprovide two fuel metering orifices having different areas at any givencorresponding fuel metering positions within the fuel metering ranges.3. A carburetor fuel metering valve according to claim 1 wherein:

said valve sleeves are relatively rotatable to three mid-range settingsto provide three fuel metering orifices having different areas at anygiven corresponding fuel metering positions within the fuel meteringranges. 4. A carburetor fuel metering valve according to claim 1wherein:

said fuel metering ports include a plurality of circumferentially spacedports in the outer valve sleeve and a port in the inner valve sleevewhich registers with the outer sleeve ports, respectively, in saidmid-range settings to provide the fuel metering orifices, each outersleeve port is totally uncovered by the inner sleeve port in thecorresponding full speed position of said valve sleeves and isprogressively covered by the inner sleeve upon relative rotation of thesleeves to the corresponding idling position, and said outer sleeveports differ in size. 5. A carburetor fuel metering valve according to35 claim 4 wherein:

said outer sleeve ports comprise slots of different width extendingcircumferentially of said outer sleeve. 6. A carburetor fuel meteringvalve according to claim 4 wherein:

said outer sleeve has two fuel metering ports, whereby said sleeves arerelatively rotatable to two mid-range settings. 7. A carburetor fuelmetering valve according to claim 4 wherein:

said outer sleeve has three fuel metering ports, whereby said sleevesare relatively rotatable to three mid-range settings. 8. A carburetorfuel metering valve according to claim 7 wherein:

said outer sleeve ports comprise slots of different width extendingcircumferentially of said outer sleeve. 9. A carburetor fuel meteringvalve according to claim 8 wherein:

said inner sleeve port has an edge which undergoes movement along eachouter fuel metering slot toward one end edge of the slot during rotationof the sleeves toward idling position at the corresponding mid-rangesetting, the fuel metering orifice at the corresponding midrange settingis formed between said port and slot edges, whereby the orifice area isprogressively reduced by said sleeve rotation to idling position, andsaid port and slot edges are oppositely inclined at oblique angles tothe common axes of the sleeves. 10. A carburetor fuel metering valveaccording to 65 claim 9 wherein:

the opposite end of each outer sleeve fuel metering slot is enlarged.

1. A carburetor fuel metering valve comprising: a pair of slidablyinterfitting valve sleeves which are relatively rotatable to a pluralityof mid-range fuel adjustment settings and are relatively rotatable ateach midrange setting through an operating fuel metering range betweenidling and full speed positions, said sleeves having fuel metering portswhich overlap at each mid-range setting to form a fuel metering orificewhose effective area is varies by relative rotation of the sleevesthrough the corresponding fuel metering range, and said sleeves beingrelatively rotatable to corresponding fuel metering positions within thefuel metering ranges and the fuel metering ports being so sized that theeffective orifice areas differ at said corresponding fuel meteringpositions.
 2. A carburetor fuel metering valve according to claim 1wherein. said valve sleeves are relatively rotatable to two mid-rangesettings to provide two fuel metering orifices having different areas atany given corresponding fuel metering positions within the fuel meteringranges.
 3. A carburetor fuel metering valve according to claim 1wherein: said valve sleeves are relatively rotatable to three mid-rangesettings to provide three fuel metering orifices having different areasat any given corresponding fuel metering positions within the fuelmetering ranges.
 4. A carburetor fuel metering valve according to claim1 wherein: said fuel metering ports include a plurality ofcircumferentially spaced ports in the outer valve sleeve and a port inthe inner valve sleeve which registers with the outer sleeve ports,respectively, in said mid-range settings to provide the fuel meteringorifices, each outer sleeve port is totally uncovered by the innersleeve port in the corresponding full speed position of said valvesleeves and is progressively covered by the inner sleeve upon relativerotation of the sleeves to the corresponding idling position, and saidouter sleeve ports differ in size.
 5. A carburetor fuel metering valveaccording to claim 4 wherein: said outer sleeve ports comprise slots ofdifferent width extending circumferentially of said outer sleeve.
 6. Acarburetor fuel metering valve according to claim 4 wherein: said outersleeve has two fuel metering ports, whereby said sleeves are relativelyrotatable to two mid-range settings.
 7. A carburetor fuel metering valveaccording to claim 4 wherein: said outer sleeve has three fuel meteringports, whereby said sleeves are relatively rotatable to three mid-rangesettings.
 8. A carburetor fuel metering valve according to claim 7wherein: said outer sleeve ports comprise slots of different widthextending circumferentially of said outer sleeve.
 9. A carburetor fuelmetering valve according to claim 8 wherein: said inner sleeve port hasan edge which undergoes movement along each outer fuel metering slottoward one end edge of the slot during rotation of the sleeves towardidling position at the corresponding mid-range setting, the fuelmetering orifice at the corresponding mid-range setting is formedbetween said port and slot edges, whereby the orifice area isprogressively reduced by said sleeve rotation to idling position, andsaid port and slot edges are oppositely inclined at oblique angles tothe common axes of the sleeves.
 10. A carburetor fuel metering valveaccording to claim 9 wherein: the opposite end of each outer sleeve fuelmetering slot is enlarged.